The present disclosure relates generally to the design, assembly, and manufacture of LED lamps and luminaires. In one aspect, the present disclosure relates to an improved LED lamp or luminaire having an overmolded LED circuit board. In another aspect, the present disclosure relates to a manufacturing method employing automation and in-mold assembly techniques during the injection over-molding of one or more of its utilized components.
LED lighting is fast becoming the desired lighting device of choice in commercial applications, municipal and government applications such as roadway and parking structure lighting and retail applications such as spot lighting and directional illumination. Compared with traditional light sources such as incandescent and fluorescent lighting devices, they have many advantages such as lower power consumption, much longer life (e.g. 50,000 hours) and no mercury or other hazardous materials in them.
Consumer household replacement lighting is an area in which LEDs are desired, but difficult to adopt because of relatively high manufacturing and component costs and problems with reliability and manufacturing repeatability. First costs of an LED replacement lamp are still upwards of 10 times that of traditional incandescent and fluorescent light bulbs. Additionally, quality issues still remain driven by assembly techniques and component and material selection. Furthermore, the advantages of long life and low power consumption are attainable only if the LED light source is kept sufficiently cool.
LED light sources generate significant thermal energy which, if not removed or managed, may prevent proper functioning, or limit the lifetime, of the source. Thermal interface and junction resistances between the heat generating LED light sources and the heat sinks of the LED lamp designed to dissipate the heat can add anywhere from 1-10 degrees Celsius or more to the LED junction temperature. Maintaining this junction temperature at or below the LED light source manufacturer's specifications is critical for the life of the LED and the lower the temperature the longer the life. According to accepted electronic design rules, for every 10 degrees Celsius temperature reduction there is a doubling of the electronic life.
Additionally, assembly of the LED lamp can significantly affect device performance, product life and product cost. In conventional hand assembly and semi-automated processes, part-to-part consistency is difficult to maintain and part-to-part reliability is compromised—especially when thermal performance is the key to success and long life for any LED lamp and poor thermal design and heat management is employed. Today's LED lights are being manufactured in component and mechanically intensive processes because of the general unfamiliarity with LED luminaire components (LEDs, drivers/power supplies, heat sinks and thermal management, optics and lenses) or with best practices for designing and assembling them together for reliable product utilization. In an LED lamp, the following manufacturing steps and components are generally needed: The heat sink to dissipate heat from the LED light source and other electronics has to be manufactured. In LED lamps and luminaires the heat sink is generally part of the housing of the product. The LED circuit board assembly has to be fabricated with all of its components including the LED light sources. This is generally done by soldering the LED light sources and any other components to traces on a PCB. In high power LED lighting, generally, the PCB is a metal core printed circuit board (MCPCB); however, other materials are used as well and in almost all cases are attached to the heat sinks and are used to conduct the heat from the LED light source to the heat sink through a thermal interface. The LED circuit board assembly has to be mounted to the heat sink. Thermal interface must be placed between the heat sink and the LED circuit board. The driver board and electronics have to be fabricated and assembled and then installed in the LED lamp. The driver board and electronics power the LED by constant current and ensure the operation of the LED light sources. The driver board is wired and assembled to the LED circuit board assembly via soldering and other connections (in some cases the drive electronics and components are mounted on the same circuit board assembly as the LED lighting devices). A lens must be manufactured and mounted to the top of the LED circuit board and in front of the lamp to focus the light from the LED light sources to the desired beam angle and intensity. A GU or Edison or other lighting industry standard connector must be wired and assembled to the drive electronics to connect the LED device to power sources. All of these assembly steps and techniques involve screws, glues, wires, soldering steps, additional parts for holding parts together and the requirement of manual labor to put everything together.
FIG. 1 illustrates an exemplary prior art LED lighting lamp employing a heat sink/housing in thermal communication with the LED circuit board and LED light source so as to provide cooling by dissipating heat into the ambient air. Connected to the LED circuit board and assembled within the LED device is the drive electronics board and connector on one side as well as the LED lens on the other.
FIG. 1 shows an exemplary LED lamp 110 having a heat sink housing 118. The housing 118 may be formed of a thermally conductive material, such as a metal or metal alloy or a thermally conductive plastic. A heat spreader plate 128 is overmolded by the thermally conductive material during an injection molding process. A drive electronics board 111 with connector attached is then physically inserted into heat sink housing 118 and mechanically screwed to the heat spreader plate 128 with connecting screws 129. A thermal interface material 131 is then mounted onto the heat spreader plate 128. Next a circuit board assembly 116 with one or more LED light sources 117 on it is physically attached to the lighting lamp 110 by placing it against the thermal interface 131 and screwing it to the heat spreader plate 128 with screws 129a. A light lens/optics 119 is then placed against the circuit board 116 and held in place by a lens cover or bezel 130 (or alternative fastener such as glue or adhesive), which is mechanically fastened to the heat sink housing 118 to hold the lens in place. An Edison or GU connector 112 is then wired to the end of the LED device 110 and attached to the drive electronics board 111.
Designing and manufacturing heat sinks for LED lamps and luminaries is not new and has been done with a number of materials to date, including thermally conductive plastics, aluminum extrusion, die casting etc. The method to manufacture the thermally conductive plastic heat sinks is typically injection molding, though other methods of forming and creating polymer shapes out of various types of polymers, epoxies and thermosetting materials is well known in the industry and injection molding process is being used as one example. All current and previous LED lights utilize a separately manufactured heat sink and then assemble the LED circuit board to the heat sink using screws, glues or other assembly mechanisms along with a thermal interface. Some products and designs do not even use a thermal interface, creating significantly poor performing products.
As a result of the lower power consumption and longer life of LED light sources, compared to traditional light sources, today's lighting market and governments worldwide are utilizing and promoting the use of high power LEDs. With government and market support, LEDs are gaining wide acceptance and adoption into mainstream lighting applications. As the global lighting requirements are continuously growing, LEDs are enabling emerging markets and underdeveloped areas to use light sources because of the low power consumption and ability for LEDs to be powered by solar energy as well as last a long time without replacement. Still, the biggest hurdle to LED lighting used in residential as replacement light bulbs on a massive scale, is the first cost to the consumer and the thermal reliability and manufacturing repeatability/cost of the lights. The Department of Energy is continuously pushing the development of LED replacement bulb devices that are energy and thermally efficient yet have the same first cost as traditional incandescent and fluorescent light bulbs.
The present disclosure describes an improved LED device design and method of fabricating the same.